1. Field of the Invention
The invention relates to printing systems which form evenly spaced indicia on a moving web at locations which are controlled by previously printed, evenly spaced web marks.
2. Description of the Prior Art
Printing systems are known which print evenly spaced indicia on a continuously moving web at locations which are controlled by previously printed, evenly spaced web marks. These systems are used for both color and non-color printing. See, for example, U.S. Pat. No. 3,152,542. Moreover, cutting systems are known which cut a continuous web into sections at locations which are determined by reference to previously printed web marks. Systems of this type may be found, for example, in U.S. Pat. Nos. 3,195,385, 3,244,863 and 4,020,406.
It is further known to obtain a larger spacing between printed indicia on the moving web than would otherwise be dictated by the dimensions of the rotary printing drum by temporarily stopping the rotation of the drum at a point of non-contact between a printing element on the drum and the moving web, and subsequently restarting the rotation of the drum. Such a system is described, for example, in U.S. Pat. No. 4,057,014. The applicants are not aware, however, of any prior art printing system which periodically stops the rotation of a printing drum and is capable of printing indicia at the same position on a moving web with respect to previously printed web marks independent of the velocity of the web. Changes in the velocity of the web often occur when the printed web is being processed into packages, such as wrappers for candy bars. Moreover, no prior art printing system which periodically stops and starts the print head is known to applicants which permits an operator to adjust the offset distance between the printed indicia and the previously printed, evenly spaced web marks independent of the velocity of the web.
Printing systems are also known which have a rotating printing drum that is mechanically driven by the motion of a web on which indicia are to be printed. These mechanical systems print indicia on the moving web at the same location independent of velocity of the web, but do not control the print locations in response to previously printed web marks.